This is a prospective clinical validation study of a novel in-vitro diagnostic (IVD) assay that will enroll 830 pediatric patients. The study will be conducted in two stages: In stage A 50 patients will be enrolled with the aim of verifying proper protocol execution including proper collection of patient samples, accurate data retrieval and precise etiology determination. In stage B 780 patients will be enrolled with the aim of blinded validation of the host-response based diagnostics using a fresh independent cohort of patients. Patients enrolling into the study will be managed according to the current standard of care (GCP) and per standard institutional procedures. Participation in this study requires the collection of an additional blood sample and a nasal swab sampling.